1. Field of the Invention
The present invention relates to a method for adjusting amplifier on/off control timing and antenna selection control timing in a radar and, in particular, in an FM-CW radar that uses a duplexer, and also relates to a radar apparatus having an automatic timing adjusting function.
2. Description of the Related Art
An FM-CW radar projects forward a transmit wave frequency-modulated by a triangular wave, produces a beat signal by mixing a reflected wave from a target with a portion of the transmit wave in a mixer, and computes the distance and relative velocity of the target simultaneously from the beat frequencies produced during the increasing section and the decreasing section of the triangular wave. Such radars are commercially implemented as automotive radars.
Japanese Unexamined Patent Publication No. 2002-122661 describes an FM-CW radar that uses a single antenna for both transmission and reception, by using a duplexer, and discloses that a bias voltage to a transmitting amplifier and a bias voltage to a receiving amplifier are turned on and off in alternating fashion in order to prevent the transmit wave from leaking into the receiving side in the duplexer and interfering with the received signal.
In this case, if the end point of the ON period of the transmitting amplifier is separated from the start point of the ON period of the receiving amplifier by, for example, 3.3 nsec or more, reflected waves from a target located within a range of 1 m cannot be captured, and thus the short-range detection performance degrades. Conversely, if the end point of the ON period of the transmitting amplifier overlaps the start point of the ON period of the receiving amplifier, the transmit signal leaks, which increases noise in the short-range detection area and may result in the detection of a false target. If the leakage of the transmit signal becomes excessively large, a device failure may result. Accordingly, the relative timing of the two amplifiers must be accurately adjusted.
Further, Japanese Unexamined Patent Publication No. H11-160423 discloses an FM-CW radar employing a DBF (Digital Beam Forming) method that sequentially switches between a plurality of receiving antennas and determines the target direction by detecting the phase difference between the reflected waves received from the same target. Japanese Unexamined Patent Publication No. 2000-155171 discloses how an effect equivalent to using more receiving antennas than actually used, can be achieved by using a plurality of receiving antennas in an DBF system. Further, though not published at the time of this patent application, Japanese Patent Application No. 2003-164122 discloses a radar apparatus that achieves further reductions in size and weight by using a plurality of antennas for both transmission and reception in a DBF system.
In connection with the foregoing, if a configuration such as shown in FIG. 1, in which a duplexer 14 is used in conjunction with a switch 12 that selects one of a plurality of antennas 10 for transmission or reception and if the on/off timing of the transmitting amplifier 16 and the receiving amplifier 18 can be adjusted accurately as shown in parts (a) and (b) of FIG. 2 by some kind of means, it is still necessary to make the timing for setting the switch 12 to select the transmitting antenna or the receiving antenna (parts (c), (d), and (e)) match the on/off timing of the transmitting amplifier 16 and the receiving amplifier 18.